Thornton Quarry operations to yield to stormwater reservoir
By Mike Nolan firstname.lastname@example.org September 23, 2013 9:00PM
When completed in late 2015, the reservoir will have the capacity to hold about 8 billion gallons of stormwater and sewage, diverting the water during storms.
The Metropolitan Water Reclamation District in 1998 reached an agreement with the quarry’s operator, Hansen Material Service, to use the north lobe of the Thornton Quarry for the reservoir. Since that time, Hansen has excavated 76 million tons of limestone from that portion of the quarry and is now wrapping up operations there.
The section the MWRD is using is a half-mile long from east to west, a quarter-mile wide from north to south, and 300 feet deep. It was briefly considered as a site for the Chicago Bears’ new stadium when the team threatened to leave Soldier Field.
Updated: October 25, 2013 6:15AM
There were muffled blasts that sounded like distant fireworks, then roughly 38,000 tons of limestone, more than 300 million years old, cascaded to the floor of the Thornton Quarry on Monday.
In a couple of years, it will be rainwater and raw sewage cascading into the enormous pit on the north side of Interstate 80.
The quarry will be a component of the Metropolitan Water Reclamation District’s expansive Tunnel and Reservoir Plan for flood control, better known as “Deep Tunnel,” which began in the early 1970s and won’t be completed until 2029.
Monday’s blast was the last extraction of limestone from that portion of the quarry, with Hanson Material Service, the quarry’s operator, wrapping up its operations in the north lobe to make way for the huge reservoir. The company will continue to mine other areas of the quarry, including the main lobe south of I-80.
For the “last blast” ceremony, officials were perched on the north rim, 300 feet above — and nearly a half-mile away — from where explosive charges had been set in the southwest corner of the quarry.
David St. Pierre, the MWRD’s executive director, on Monday called Deep Tunnel “one of the most visionary projects” in the country. The nickname came about because some of the system’s giant tunnels run hundreds of feet below ground.
The MWRD estimates that, systemwide, Deep Tunnel will save more than $130 million annually in flood-related damage costs.
“We still get people from all over the world who come out and look at what we’ve done” as they plan similar flood control systems, St. Pierre said.
The $430 million Thornton Reservoir will provide flood protection to more than a half-million residents, according to the MWRD. The reservoir in the north lobe of the quarry is expected to be ready by the end of 2015.
The Thornton Reservoir will be able to hold nearly 9 billion gallons of water. A quarry in McCook that’s also part of Deep Tunnel will eventually have a capacity of 10 billion gallons, St. Pierre said.
Since 2003, the district has used a portion of the Thornton quarry, west of the main lobe, as a temporary reservoir for stormwater. It will no longer be used for that purpose once the permanent reservoir is finished.
Work continues on huge tunnels that will divert stormwater and, in some instances, sewage, into the Thornton Reservoir. That’s because some communities on Chicago’s South Side and the south suburbs the reservoir will benefit do not have separated sewer lines, said John Lemon, principal civil engineer with the MWRD.
Water held in the reservoir will be pumped to the MWRD’s Calumet treatment plant near 130th Street and the Bishop Ford Freeway.
In 1998, the MWRD reached an agreement with Hanson Material Service so it could use the north lobe for the Thornton Reservoir. With Monday’s “last blast,” Hanson pulled about 76 million tons of limestone from that section since the agreement and will begin concluding mining operations there to allow the MWRD to finish its work.
The north lobe is a half-mile in length from east to west, a quarter-mile wide north to south and 300 feet deep. It was, albeit briefly, considered a potential site for the Chicago Bears’ stadium when the team threatened to bolt from Soldier Field.
“It has been a long journey to get to this point,” Jeff Brasuell, Hanson’s area operations manager, told officials gathered for Monday’s ceremony.
The area the MWRD will use represents a “fraction of the overall quarry,” he said. Hanson, which bought the quarry’s former operator, Material Service Corp., will continue to mine in other sections, Brasuell said.
“We will continue to do what we do day in and day out,” he said.
Limestone mined from the quarry is used in applications such as concrete and asphalt, and Brasuell said that the rock can be found in roads, home foundations and other structures throughout the Southland.